The present invention concerns a cutting press, especially one used for cutting sheet or weblike matter to be converted into a package.
For the cutting action, the upward and downward motion of a lower beam of such a press can be achieved by means of a system comprised of four crankshaft and pull-rod units, or of four toggle lever and cam units. The upper dead center of the drive system corresponds to the processing, e.g. cutting position of the press, in which the tool counter-part fitted on the movable lower beam is pressed against the tool fitted on the upper beam.
For increasing productivity, such presses are designed in such a way that on the occasion of a same processing action, several blanks of identical shape and dimensions may be obtained simultaneously from a single sheet, the total surface of which is at least equal to the sum of all blanks. This means that the tool and the tool counter-part are both of platelike, generally rectangular, shape of large dimensions, carrying the processing tools on one of its sides, the other side being in contact with a side of the corresponding beam, which side, though, has a surface at least equal to, if not larger than, the tool surface or counter-part tool surface of the tool.
Considering that a perfect parallelism between the tool and the tool counter-part is the primary condition for obtaining a dependable cutting throughout the surface of the cardboard sheet to be cut out, the condition can be fulfilled only if the two beam surfaces carrying the tools and the tool counter-parts, i.e. the processing areas, are perfectly parallel to one another, at least during the cutting action, i.e. when the drive system is situated in an upper dead center position.
With a view to achieving the parallelism of the two beams, the Swiss Patent CH-A-57814 has proposed to act on the four bearings holding the crankshaft and pull-rod units on the lower crossbar of the press frame. The bearings are fitted so as to be shiftable vertically by means of various trapezoid wedges arranged pairwise between the various bearings and the bottom of a sliding rail in the lower crossbar. By shifting the wedges, it is possible to vertically vary the position of the bearings and, thereby, of the lower movable beam. Adequate regulation of the height of the four bearings will thus permit an initial parallelism which will later on have to be perfected by a so-called make-ready operation comprised of adding short bits of narrow adhesive paper on the back side of the tool opposite the cutting rules or other processing organs so as to compensate a residual deficiency of parallelism as well as shortcomings caused by the cutting rules. However, the make-ready operation has the disadvantage of requiring much working time and the involvement of human know-how.
The Swiss Patent CH-A-652967 describes a cutting press of which the drive system of the movable lower beam consists of a system with four toggle lever and cam units. The parallelism between the two beams is achieved by means of a single wedge inserted between the toggle lever bearings and the lower crossbar of the frame. In such a case, the make-ready operation is also necessary.
Moreover, considering that a cutting press is also designed so as to enable the same tool to be used for sheets of different dimensions, certain sheets might cover generally only part of the total tool area. So, on account of the fact that the sheet is generally arranged during the cutting action at the downstream end of the tool when referring to the sheet travelling direction, this partial occupation of the processing area of the tool causes uneven application of the cutting pressure with the unevenness propagating to the lateral posts of the frame. This causes different values of lengthening there among them and thus a lack of parallelism between the two beams.
The unevenness of the pressure applied, though, has the serious inconvenience of causing rapid wear and tear of the cutting rules.
For compensating this unevenness, users generally resort to the above-mentioned make-ready method as well as to at least one compensating die containing some cutting rules or other processing devices and fitted at the upstream end of the tool so as to obtain full parallelism of the tools. Nonetheless, even in such a case, the make-ready operation would lead too far.
As happens frequently with a cutting press processing sheets of a partial size, it is obvious that with the make-ready operation discarded, or at least reduced to a mere minimum, a considerable amount of time would thus be saved when preparing the tool.